vV^ 

& % 



n j?\ 






^ 



**cs5jj^ju** v x o * jtefllfc?* *J . **£* .sF$Sfo^ *. r "f A A ° £Mm%>+^ u -** <^ * \s*$Sw ":. «7 a , ° 



» o 



V 


















^% 






•z V"V 




V, 



\rv 





■ V cO«o«/V * * * O* V l, vo° • * V <-°» G «*% 







■\r<S 3 



VV 






^* * o fi V> *n * 








** V \ 



Vj. 

















$*, o 






%o^ 



^ ^ 



^/-o^ 



^ 






>„*» 







^-^.^X w X-vA>^^^^ 






o<- -^-^>.X*' - 5C- -x-"*^.^ 






w ; 














s > v 











' ^«\ 











• S ^° 



»P<I. 






























^>o^ 



^o^ 



/5\.^ 



8b- "W 







Bureau of Mines Information Circular/1987 



Corrosion of Friction Rock Stabilizer Steels 
in Underground Coal Mine Waters 



By A. F. Jolly III and L A. Neumeier 




UNITED STATES DEPARTMENT OF THE INTERIOR 




w* 






Information Circular 9159 

K ^ 



Corrosion of Friction Rock Stabilizer Steels 
in Underground Coal Mine Waters 



By A. F. Jolly III and L. A. Neumeier 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 

David S. Brown, Acting Director 







Library of Congress Cataloging in Publication Data: 



Jolly, A. F. (A. Fletcher) 

Corrosion of friction rock stabilizer steels in underground coal mine 
waters. 

(Bureau of Mines information circular ; 9159) 

Bibliography: p. 13 -- 14. 

Supt. of Docs, no.: I 28:27: 9159. 

1. Mine roof bolting. 2. Rock bolts -Corrosion. 3. Mine water. 4. Steel alloys-Corro- 
sion. I. Neumeier, L. A. II. Title. III. Series: Information circular (United States. Bureau of 
Mines) ; 9159. 

TN295.U4 [TN289.3] 622 s [622'.8] 87-600138 



CONTENTS 



Page 



Abstract 1 

Introduction 2 

Experimental procedure 3 

Results and discussion 6 

Conclusions 12 

References 13 

ILLUSTRATIONS 

1. Closeup of corrosion cell and specimen holder used with electrochemical 

test equipment 5 

2. Examples of pitting scans 11 

TABLES 

1. Sources of coal mine waters used in testing 3 

2. High-strength, low-alloy steel compositions 6 

3. Chemical analyses of underground coal mine waters 7 

4. Electrochemically derived corrosion rates in underground coal mine waters. . 8 

5. Corrosion rates of HSLA Split Set steels in underground coal mine waters... 10 

6. Pitting tendency of HSLA and galvanized steels in underground coal mine 

waters 12 





UNIT OF 


MEASURE 


ABBREVIATIONS 


USED IN THIS REPORT 


°F 


degree Fahrenheit 


nA/cm 2 


nanoampere per square centimeter 


h 


hour 




ppm 


part per million 


in 


inch 




rpm 


revolution per minute 


mL 


milliliter 




V 


volt 


mpy 


mil per year 




wt pet 


weight percent 



CORROSION OF FRICTION ROCK STABILIZER STEELS 
IN UNDERGROUND COAL MINE WATERS 

By A. F. Jolly III 1 and L. A. Neumeier 2 



ABSTRACT 

In an effort to better predict the useful service life of friction 
rock stabilizer mine roof bolts in coal mine environments, the Bureau of 
Mines has evaluated the corrosion resistance of stabilizer steels in 
air-saturated and deaerated waters from seven Eastern and Midwestern 
underground coal mines. Accelerated electrochemical corrosion tests 
were used to estimate corrosion rates for the two high-strength, low- 
alloy (HSLA) steels used to fabricate Split Set stabilizers and for gal- 
vanized steel. Long-term static-immersion weight-loss tests were also 
conducted with the HSLA steels. 

Corrosion rates developed from the weight-loss tests (steady-state air 
dissolution) were roughly comparable to rates determined from electro- 
chemical testing in aerated waters. Although the highest rates occurred 
in waters with the highest chloride contents, rates in the other waters 
were low (<2.0 mpy) and exhibited little correlation to the widely var- 
ied chloride contents of the waters. The generally low corrosion rates 
are attributed in part to the tendency to deposit a protective CaC0 3 
film, reflecting susceptibility to carbonate precipitation as indicated 
by positive Langelier (saturation) index values for the waters. With 
one exception, corrosion rates for the galvanized steel were <2.0 mpy. 
Rates with aerated waters were higher than those with deaerated waters. 
Pitting tendencies of the steels were also estimated. 



"1 Metallurgist. 
^Supervisory metallurgist. 
Rolla Research Center, Bureau of Mines, Rolla, MO. 



INTRODUCTION 



The friction rock stabilizer represents 
a new concept in roof -rock bolting which 
has become increasingly popular since its 
first commercial introduction during the 
1970 f s. Friction rock stabilizers are 
thin-walled tubular devices which, upon 
installation, exert their holding power 
by exerting forces over the entire length 
of the stabilizer. Unlike conventional 
point-anchor bolts, friction rock stabi- 
lizers can continue to hold when rock 
strata shifts, a circumstance that some- 
times loosens or breaks conventional 
bolts. Friction rock stabilizers are 
particularly useful in softer rock such 
as shale and sandstone. However, due to 
their thin-wall construction, and the re- 
latively large-surface area exposed to 
potential corrosive attack, friction rock 
stabilizers are more susceptible than 
solid bolts to damage by corrosion; con- 
sequently, they are not normally recom- 
mended for long-term use. 

The Split Set 3 stabilizer, one of se- 
veral types of these friction rock sta- 
bilizer devices, has gained widespread 
adoption in the metal mining industry. 
More than 28 million Split Set stabili- 
zers have been installed worldwide, pri- 
marily in metal mines, but also exten- 
sively in coal mines in the Republic of 
South Africa. The Split Set stabilizer 
is a longitudinally slotted tube, with a 
ring welded on one end to secure a base 
plate; its diameter is 1-1/2 in or 
larger. In use, the Split Set stabilizer 
is forced into an undersized drilled 
hole. The stabilizer undergoes elas- 
tic deformation from which the tube at- 
tempts to recover, thereby generating 
compressive stresses in the surrounding 
rock strata along the entire length of 
the stabilizer. 

Split Set stabilizers are made of steel 
sheet, about 0.1 in thick, and are pro- 
duced in various lengths. They are also 
available hot-dip galvanized (with a 



~0.0025 in coating). Two types of HSLA 
steels are used to manufacture Split Set 
stabilizers, KAI-WELL-55 steel from Han- 
nibal Industries, Los Angeles, CA, and 
EX-TEN-H60 from the Bristol Steel Corp,, 
Bristol, PA. 

This report discusses the corrosion re- 
sistance of Split Set stabilizers in 
underground coal mine waters. This work 
is a continuation of earlier research, 
which investigated the susceptibility of 
Split Sets to corrosion in U and Cu mine 
waters of the Western United States (15)4 
and in Missouri Pb and Fe mine waters 
(16). The earlier research involving U 
and Cu mine waters demonstrated that the 
corrosion of roof support steels is 
highly variable and difficult to predict 
without empirical data for comparative 
purposes, given the diversity of mine 
environments where Split Set stabilizers 
are commonly employed. Corrosion rates 
for the steels in Missouri mine waters 
were generally much lower, particularly 
for the Pb mine waters. 

A nondestructive test to verify the 
holding power of installed friction rock 
stabilizers is not available. Bureau of 
Mines research has resulted in the de- 
velopment of a device to verify proper 
Split Set installation, based on internal 
volume measurements (11). However, there 
is no way to measure the extent of de- 
gradation due to corrosive attack. The 
results of this and related investiga- 
tions are intended to assist both mining 
industry personnel and the Mine Safety 
and Health Administration (MSHA) to bet- 
ter evaluate what constitutes a safe 
service life for friction rock stabili- 
zers. 

At the present time, the use of Split 
Set friction rock stabilizers in under- 
ground coal mines is limited. The deve- 
lopment, by Inge rs oil-Rand, of a compati- 
ble percussive bolt driver for electrical 
drilling equipment (12), has provided 



J Registered trademark of Ingersoll- 
Rand Co. Reference to specific products 
does not imply endorsement by the Bureau 
of Mines. 



Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this report. 



opportunity for increased usage of fric- 
tion rock stabilizers in coal mine envi- 
ronments. Recent Bureau studies ( 13 ) 
into the relationship of geology to coal 
mine roof stability have concluded that 
fluctuating seasonal humidity has a sig- 
nificant effect on roof-fall occurrences 



and rates. This variable humidity and 
resultant seepage also promote corrosion. 
The Bureau undertook the investigation 
reported here to study the potential de- 
leterious effects of corrosion on steel 
friction rock stabilizers. 



EXPERIMENTAL PROCEDURE 



Flat sheet samples of the steels used 
in Split Set friction rock stabilizers, 
Bristol's EX-TEN-H60 and Hannibal's KAI- 
WELL-55 were analyzed to determine con- 
formance with manufacturers' specifica- 
tions. A metallographic evaluation of 
these steels, together with illustrations 
of typical microstructures, is contained 
in an earlier Bureau report (15). 

Galvanized Split Set stock was not 
available in flat-sheet form, since the 
Split Set stabilizers are hot-dip galvan- 
ized only after fabrication. Because the 
corrosion-cell specimen holder would ac- 
cept only flat specimens, samples cut 
from the galvanized stabilizers were 
flattened to eliminate curvature. Unfor- 
tunately, flattening the curved samples 
destroyed the integrity of the galvanized 
coating; consequently, galvanized plain- 
carbon steel in flat-sheet form was used 
for corrosion testing instead of galva- 
nized Split Set stabilizer steel. 

The use of plain-carbon galvanized 
steel sheet in place of actual galvanized 
stabilizers was judged to be acceptable, 
since variation in the composition of the 
outermost Zn layer of galvanized coatings 
is minimal. Such compositional varia- 
tion, if detectable, has been found to 



have an insignificant effect on corrosion 
rates (2_, p. 712; J}, p. 646). 

The scope of this research did not in- 
clude the complex situation where cor- 
rosion penetrates the Zn coating. Such 
penetration eventually results from ex- 
tended exposure to a corrosive environ- 
ment. Alternately, penetration of the Zn 
coating could result from mechanical dam- 
age to the coating during installation, 
such as when the stabilizer is forced 
into a smaller than specified drill hole. 
In either event, should the coating be 
penetrated, the Zn will continue to pro- 
vide sacrificial protection to the ex- 
posed steel until a considerable amount 
of coating has been consumed. 

Twenty-liter samples of mine water were 
collected from seven underground coal 
mines, three in the Midwest and four in 
the East. (See table 1.) Friction rock 
stabilizers have not been used on a pro- 
duction basis in the mines from which the 
waters were obtained. 

All mine water samples were collected 
directly from roof seepage or from 
sources in active faces. No samples were 
taken from water that had collected on 
mine floors, which was more likely to be 
contaminated. The percolated waters were 



TABLE 1. - Sources of coal mine waters used in testing 



Mine 


Location 


Ownership 


Midwestern: 






Peabody No. 10.... 


Christian and Sangamon 
Counties, IL. 


Peabody Coal Co. 




Washington County, IL. 
Randolph County, IL... 


Do. 




Do. 


Eastern: 




Somerset No. 60. . . 


Washington County, PA. 


Bethlehem Mines Corp. 




Indiana County, PA.... 


Keystone Mining Co. 


Bureau of Mines 


Allegheny County, PA.. 


U.S. Government. 


Experimental. 










Peabody Coal Co. 



relatively low in ferric sulfate content, 
which is uncharacteristic of stagnant 
coal mine waters that have been exposed 
for substantial periods in contact with 
pyritic materials under an oxidizing 
environment. Mine water temperatures 
were measured on-site. 

Samples were subsequently analyzed to 
determine chemical composition, and pH 
values. Langelier indexes, which indi- 
cate the relative tendency for CaC0 5 to 
precipitate from water and form a 
protective film on metal surfaces, were 
calculated using the values for the 
Ca, bicarbonate, and total dissolved 
solids contents, and the pH factor and 
temperature. 

Corrosion rates of the EX-TEN-H60 and 
KAI-WELL-55 steels were measured using 
both "instantaneous" electrochemical 
methods and long-term static-immersion 
weight-loss techniques. Corrosion rates 
of galvanized steel were measured by 
electrochemical methods only. 

The purpose of the static weight-loss 
tests was to provide corrosion rates that 
could be compared with those obtained by 
accelerated electrochemical testing, the 
primary research method. The static- 
immersion determinations of corrosion 
rates from weight-loss data were done in 
accordance with The American Society for 
Testing and Materials (ASTM) Standard 
G31-72, "Laboratory Immersion Corrosion 
Testing of Metals" (5). Test specimens 
of the EX-TEN-H60 and KAI-WELL-55 steels 
with an approximate surface area of 2 
square inches were machined from sheet 
stock. Specimens were suspended in the 
test solution by a nylon filament that 
passed through a small hole drilled 
through one edge of the test coupon. 
After polishing on 120-grit SiC abrasive 
paper, the specimens' dimensions were 
measured and precise surface areas were 
calculated. After cleaning in ethanol, 
the specimens were weighed. Two speci- 
mens of each steel were suspended in each 
mine water. 

The mine waters utilized in the weight- 
loss tests were contained in 1,000-mL 
beakers immersed in a constant-tempera- 
ture bath at 55±5° F, the average of the 
actual temperatures measured in the 
mines. The actual in-mine temperatures 



ranged from 52° to 59.5° F. (Samples were 
collected in November and December. ) 
During the weight-loss tests, beakers 
were loosely covered, permitting access 
of air. The test solution temperatures 
and dissolved oxygen contents were moni- 
tored daily. No attempt was made to con- 
trol the dissolved oxygen content, which, 
within 100 h of test initiation, fell 
from total saturation values to steady- 
state (typically about 2 ppm below sat- 
uration) for the duration of the test. 
The weight-loss corrosion tests were ter- 
minated after 3,028 h (approximately 
126 days). The specimens were scrubbed 
with a bristle brush under running water 
to remove loosely adherent corrosion pro- 
ducts, dried in a warm air blast, and 
weighed. Corrosion rates were calculated 
from the measured weight losses. 

The accelerated electrochemical cor- 
rosion tests were performed using a 
microprocessor-based corrosion measure- 
ment system (14). This system consists 
of a corrosion cell and supporting 
instrumentation. The cell (fig. 1), con- 
taining test solution, specimen, counter- 
electrodes, and a standard calomel refer- 
ence electrode, is immersed in a 
controlled-temperature water bath. The 
microprocessor unit was used to define 
and control the experiment, take measure- 
ments, store data, and calculate and 
print the results. 

Corrosion rates were determined using 
the linear polarization (polarization re- 
sistance) technique. First, anodic and 
cathodic polarization plots were genera- 
ted, from which Tafel constants (slopes) 
were determined. Using these Tafel con- 
stants, corrosion current and subse- 
quently corrosion rate were calculated 
from the slope of the linear polarization 
plot. A more detailed discussion of the 
technique employed and the electrochem- 
ical test equipment utilized can be found 
in earlier Bureau reports (15-16). 
Other descriptions of accelerated elec- 
trochemical measurements and projections 
of estimated corrosion rates are found in 
numerous references, some of which are 
cited herein (1_, 4^, 6^, 10). 

All electrochemical corrosion testing 
was conducted at the previously measured 
in-mine water temperatures. Oxygen con- 




FIGURE 1.— Closeup of corrosion cell and specimen holder used with electrochemical test equipment. 



in both air-saturated (aerated) waters 
and in helium-degassed (deaerated) 
waters. All mine waters were stirred at 
about 100 rpm during the electrochemical 
data mesurements. 

Since localized pitting was observed 
during some of the electrochemical and 
weight-loss corrosion tests, a series of 
electrochemical pitting susceptibility 
scans was made for both the KAI-WELL-55 
and galvanized steels. Using the cyclic 



polarization technique, these pitting 
scans were run for six of the mine waters 
evaluated, for both the air-saturated and 
deaerated conditions. As with all other 
electrochemical tests, the pitting scans 
were run at the measured in-mine water 
temperatures. 

Chemical analyses of the steels and wa- 
ters were conducted using essentially 
conventional procedures. 



RESULTS AND DISCUSSION 



Chemical analyses of the HSLA steels 
used in the manufacture of Split Set sta- 
bilizers are shown in table 2. The com- 
positions of both the EX-TEN-H60 and KAI- 
WELL-55 steels evaluated in the current 
investigation were found to be within the 
manufacturer's specifications. The most 
significant difference between these two 
steels is the Cu content; KAI-WELL-55 
steel has a minimum Cu content of 0.20 
wt pet, whereas Cu content is not speci- 
fied for the EX-TEN-H60. The actual Cu 
contents of the HSLA steels utilized in 
the investigation were 0.32 and 0.01 
wt pet for the KAI-WELL-55 and EX-TEN-H60 
steels, respectively. 

Chemical analyses of the seven mine wa- 
ters studied are given in table 3. Mine 
waters from all three of the Illinois 
mines and from one of the Pannsylvania 
mines (Somerset No. 60) were quite high 
in Na and CI contents. In the Illinois 



mine waters, the Na + ion content varied 
from 1,030 to 6,900 ppm, and the CI" ion 
content varied from 1,000 to 12,200 ppm. 
In contrast, the Na + and CI" ion contents 
of the water from the Robinhood No. 9 
Mine (West Virginia), were as low as 0.8 
and 3. 2 ppm, respectively. The water 
samples from two mines, the Peabody No. 
10 Mine (Illinois), and the Bureau's Ex- 
perimental Mine (Pennsylvania), contained 
large amounts of Ca and Mg. Bicarbonate 
ion content was high in samples from the 
Marissa, Baldwin (both in Illinois), and 
Somerset No. 60 Mines. Sulfate ion con- 
tent was highest, by far, in samples from 
the Urling No. 1 Mine, and the Bureau Ex- 
perimental Mine, both in Pennsylvania. 
All of the waters analyzed low in Fe, <1 
ppm. Total dissolved solids ranged from 
20, 000 ppm for the water from the Peabody 
No. 10 Mine (which had the highest Na and 
CI contents) to as low as 352 ppm for 



TABLE 2. - High -strength, low-alloy steel compositions, 
weight percent 



Element 


EX-TEN-H60 


KAI-WELL-55 




Specification ' 


Analysis 


Specification^ 


Analysis 


Cu 

Mn 


Max 0.25 

( 3 ) 

NS 

Max 1.35 

Max .012 

NS 

NS 

NS 

( 3 ) 


0.23 
.01 
.01 

1.22 

NA 

.02 

.02 

<.02 
.01 


0.2 -0.3 

NS 

Min .20 

.85-1.30 

NS 

Max . 05 

Max . 05 

Max . 1 2 

NS 


0.3 

NA 

.32 

1.12 

NA 

.02 

.02 

<.02 

NA 



NA Not analyzed. NS Not specified. 
'Woldman (L7., p. 435). 
2 Ingersoll-Rand Co. (9). 
Specification minimum 0.02 wt pet Cb + V. 



CD 
U 

■u 
co 

<D 

C 
1 



CO 
O 
O 

T3 

C 
3 
O 
u 
bO 

Ui 
0) 
T3 

3 
3 

<4-l 

o 

CO 
<D 
CO 

>> 

r-l 
CO 

a 

CO 



CO 

u 



w 
« 



t-l 


















<u 














•H X 














M CU 


\£> 


■<r 


m 


m 


1— I 


00 —1 


CD X) 


• 


• 


• 


• 


• 


• • 


bO 3 


o 


—i 


+ 


i— i 


+ 


+ + 


3 -H 


+ 


+ 




+ 






3 
















1—1 


CN 


r— 1 


m 


on 


00 l-» 


w 


• 


• 


• 


• 


• 


• • 


a 


r->- 


oo 


CO 


00 


r^ 


r^ r~- 






o 


CN 


o 


o 


o 


O CN 






o 


CN 


<f 


o 


00 


o m 




CO 


o 


vD 


•—1 


o 


oo 


o en 




Q 


* 


*1 


^ 


^ 




„ 




H 


o 

CN 


O 


en 


CN 




i-H 


iH 








o 




O On 




CO 








• 




• • 




4-1 CO 


O 


o 


o 


en 


r--» 


oo m 




O 


i—l 


— 1 


i—i 




vD 


vO en 




H 


V 


V 


V 






















nO 






■* 












• 






o 


O 


o 


o 


r>^ 


r^ 


O ON 






00 


i— I 


r~ 1 


~H 




nO 


r^ oo 








V 


V 


V 




1— 1 


i-H 


K1 


-* 


00 


-3" 


CN 


in 


en cn 






O 


• 


• 


• 


• 


• 


• • 






z 


CN 


-H 


^ 


~H 




1—1 !—) 




CN 


sD 


o 


o 


o 


o <r 




co 


r^ 


r^ 


O 


CO 


SO 


r-^ 


vo m 




3 


O 


en 


o> 


o 


as 


CN 


CM ^H 




o 


CJ> 






*l 


^ 








•H 


sc 






—I 


■—I 








fl 




































O 


^D 


en 


<r 


vO 


CN en 


s 




fa 


• 


• 


• 


• 


• 


• • 


p. 






m 


<r 


en 


vD 




































CM 


4J 
















• 


s 






o 


o 


o 


O 


00 


en en 


a> 




H 


o 


o 


o 


O 


-tf 


00 


4-1 




U 


CN 


r— 1 


o 


O 


•— i 


CM 


3 






r. 


„ 


„ 


„ 






o 






CN 


vO 


r-< 


vO 






u 






i—l 


























O 00 


















• • 








O 


o 


o 


o 


vO 


r-^ 






CO 


O 


m 


m 


ON 


r-^ 


en 






z 


ON 


en 


o 

.— i 




CN 










.— t 




v£> 


-H <r 












• 




• 


• • 






bO 


CN 


00 


<r 


m 


sT 


N43 00 






S 


•— 1 


en 




en 




r^. —i 




CO 




i—l 














3 
o 
































•H 






r^ 


r-~ 




O 


ON o 




4J 






• 


• 




• 


• • 




CO 


w 


o 


r^ 


m 


^o 


CN 


en en 




u 




en 


i—i 




•—1 








-* 


CN 


o 














i—i 


~H 


■— t 












0) 


• 


• 


• 












fa 


o 






— i 

V 


■—1 
V 


V V 




o 


o 


a-s 


O 


CN 


O 00 






CO 


o 


m 




en 


CN 


r^ <!• 






C_> 


en 










i—i 




m 






• 


• 


• • 




• 






• 


• 


• • 




• 






• 


• 


• • 




• 






o 


• 


CO • ON 




o 






vO 


• 


<u . 




-H 






• 


• 

i-H 


C H , 
•H CO O 


CD 


• 






o 




2 4-» Z 


a 


o 






z 


• 


3 


•H 


z 








o 


lt-| CD T3 


g 








4-> 


z 


o e o 




>> 


CO 


3 


a) 




•H O 




X) 


co 


•<-i 


to 


bO 


3 H£ 




o 


CO 


3 


u 


3 


co en a 




Xi 


■H 


T3 


<u 


•H 


<u ex -h 




CO 


V-l 


H 


S 


.-H 


u X XJ 




at 


CO 


CO 


o 


U 


3 w o 








fa 


S 


PQ 


CO 


£3 


« OS 



the water from the Robinhood No. 9 Mine 
(lowest Na and CI contents). All of the 
waters were somewhat basic. With the ex- 
ception of the Peabody No. 10 water, pH 
values ranged between 7.7 and 8.5; Pea- 
body No. 10 water had an almost neutral 
pH of 7.1. 

The Langelier index, also called the 
saturation index, was calculated for each 
of the seven mine waters evaluated (table 
3). The Langelier index is essentially 
a measure of the tendency for the 
precipitation-disposition of a thin CaC0 3 
scale on a metal surface. Mine waters 
commonly contain dissolved Ca and Mg 
salts in varying concentrations, de- 
pending on the source and location of the 
water. Harder waters contain more dis- 
solved salts, and hence may have an in- 
creased tendency to deposit a thin pro- 
tective coating of CaC03 on the corroding 
metal. When present, the CaC0 3 film 
forms a barrier to the diffusion of dis- 
solved oxygen to cathodic areas, slowing 
the rate of attack. The result is that 
harder waters are generally less corro- 
sive than softer waters, in which such 
protective films do not tend to form. 
The ability of CaC0 3 to precipitate on a 
metal surface depends, however, on more 
than water hardness alone. The total 
acidity or alkalinity (pH) and total dis- 
solved solids also affect the tendency 



toward the film formation. The Langelier 
index relates all these variables, and 
can be defined as the difference between 
the measured pH of a water and the equi- 
librium pH for CaC0 3 (that pH at which a 
given water is in equilibrium with solid 
CaC0 3 , with neither dissolution nor pre- 
cipitation occurring). 

Calculated Langelier indexes for the 
tested mine waters ranged from +0.1 to 
+1.5. A positive index indicates that 
the water is supersaturated with CaC0 3 
and that CaC0 3 may be expected to deposit 
on the metal surface. When the Langelier 
index exceeds ~+0.5 at temperatures typi- 
cal of those encountered in coal mine wa- 
ters, corrosion may normally be expected 
to decrease (provided that oxygen content 
and other variables are essentially con- 
stant). 

Results of the electrochemical corro- 
sion tests indicate that KAI-WELL-55 
steel exhibits, on the average, slightly 
lower corrosion rates than does EX- 
TEN-H60 steel (table 4). KAI-WELL-55 
steel was also found to be more corrosion 
resistance in earlier studies of these 
same steels in western Cu and U mine wa- 
ters (15), as well as in Missouri Pb and 
Fe mine waters (16). The somewhat better 
corrosion resistance of KAI-WELL-55 steel 
is attributed to its Cu content. 



TABLE 4. - Electrochemically derived corrosion rates in underground 
coal mine waters 





Test 
solution 
temp, °F 


Oxygen 
content, 1 
ppm 




Corrosion rate, 2 


mpy 


Mine 


EX-TEN-H60 


KAI-WELL-55 


Galvanized 




Av 


a 


Av 


a 


steel 




Av 


0" 




59.5 
59.5 
59.0 
59.0 
58.5 
58.5 
52.0 
52.0 
57.0 
57.0 
52.0 
52.0 


9.4 
<.2 
9.6 
<.2 
9.3 
<.2 

10.3 
<.2 
9.8 
<.2 

10.5 
<.2 


8.7 

1.2 

1.9 

.7 

.9 

.4 

.6 

.4 

1.7 

1.0 

1.8 

1.9 


2.1 
.2 
.2 
.2 
.2 
.2 
.1 
.1 
.2 
.05 
.2 
.4 


6.8 

1.0 

2.0 

.7 

.7 

.2 

.6 

.4 

1.6 

.8 

.9 

.9 


0.6 
.2 
.9 
.2 
.1 
.1 
.1 
.1 
.2 
.1 
.1 
.1 


1.8 

1.3 

2.0 

1.2 

1.5 

.4 

3.3 

.8 

1.7 

.2 

.7 

.3 


0.8 
.6 
.2 




.5 
.7 




.1 
.9 
.5 
.6 




.1 
.1 




.1 



'Higher values are air-saturated; the 
2 o standard deviation. 



<0.2 values are deaerated. 



As expected, corrosion rates for both 
HSLA steels were generally higher in air- 
saturated waters than in deareated 
waters, owing to the increased oxygen as- 
sessibility. Overall, corrosion rates 
were generally lower than expected, given 
the high chloride content of some of the 
waters. All experimentally determined 
corrosion rates for both HSLA steels in 
both air-saturated and deaerated solution 
fell within the relatively narrow pro- 
jected range of 0.2 to 2.0 mpy, with the 
notable exception being the rate for the 
water from the Peabody No. 10 Mine (table 
4). With this exception, the corrosion 
rates in relatively pure mine waters were 
not dramatically different from those in 
the mine waters with high chloride 
contents. 

Given the considerable variation in 
chemistry of these diverse mine waters, 
more variation in corrosion rate might be 
expected. Since little variation was ob- 
served, the investigators deduced that 
two or more different mechanisms were 
evidently in operation such that there 
was an "artificial" leveling of the cor- 
rosion values obtained experimentally. 
The explanation for this relative uni- 
formity of corrosive attack in waters of 
substantially varying compositions is 
thought to lie in the selective deposi- 
tion in most of the mine waters of a 
CaC0 3 film on the surface of the cor- 
roding sample. Formation of such a pro- 
tective film would result in a sharply 
reduced corrosion rate, because the kine- 
tics of the corrosion reaction would be 
controlled by diffusion rates through the 
CaC0 3 film barrier. Some varying amount 
of Fe-oxide-bearing passivation film 
might also have formed with the different 
waters, which would also indicate a dif- 
fusion controlled reaction. The precise 
reaction mechanisms were not determined. 

Positive Langelier indexes suggest that 
formation of a protective film of CaC03 
probably occurred for all mine waters 
studied except those from the Urling No. 
1 and Robinhood No. 9 Mines (the two mine 
waters with the lowest total dissolved 
solids). Both of these waters had a 
Langelier index of +0.1, which indicated 
only a slight tendency toward carbonate 
precipitation. The sole exception to the 



observed clustering of corrosion rates 
between 0.2 and 2.0 mpy was the case of 
the air-saturated water from the Peabody 
No. 10 Mine. In this medium, the HSLA 
projected corrosion rates were much 
higher — 8.7 and 6.8 mpy for the 
EX-TEN-H60 and KAI-WELL-55 steels, re- 
spectively (table 4). The water from the 
Peabody No. 10 Mine was extremely high in 
Na and CI (6,900 ppm Na; 12,200 ppm CI; 
20,000 ppm total dissolved solids), con- 
taining roughly twice the dissolved 
salt as found in the water with the next 
highest chloride content. Although mine 
water from the Peabody No. 10 Mine had a 
positive Langelier index of +0.6, indica- 
ting that carbonate precipitation should 
occur, it is believed the sample surface 
was attacked so rapidly as to prevent the 
formation of a protective film having 
high integrity. Thus, the corrosion re- 
action in air-saturated water from the 
Peabody No. 10 Mine was not exclusively 
diffusion controlled, as was thought to 
be the case with other mine waters where 
CaC03 film formation occurred. 

The Langelier index, although useful as 
a predicitive estimator of relative cor- 
rosion tendency, does not always relate 
to actual behavior in a reliable or con- 
sistent manner. The mine water with the 
highest Langelier index, +1.5, for the 
sample from the Somerset No. 60 Mine, 
produced some of the lowest corrosion 
rates observed during this series of ex- 
periments. In contrast, Marissa mine 
water also had a high Langelier index 
(+1.4), but corrosion rates were signifi- 
cantly higher than the index would sug- 
gest. High chloride, a condition en- 
countered in the waters from both the 
Somerset No. 60 and Marissa Mines, in 
combination with the other water vari- 
ables, can significantly affect the ac- 
curacy of the Langelier index as a pre- 
dictive model (]_)» 

Higginson (8) has suggested that dis- 
solved oxygen content and pH are the main 
factors controlling the corrosion of mild 
steel in South Africa mine waters (sim- 
ilar in chemistry to those studied here- 
in). In the pH range of interest herein 
(slightly alkaline) Higginson found that 
corrosion rate is essentially independent 
of pH and is mainly controlled in both 



10 



air-saturated and deaerated waters by the 
mass transport of H and dissolved oxygen 
to the metal surface with oxygen reduc- 
tion in cathodic regions. The higher ac- 
cess of oxygen in air-saturated waters 
leads to generally higher corrosion rat- 
es. Although he found some evidence of a 
Langelier effect, particularly in deaer- 
ated mine waters with pH values above 
7.5, Higginson believes that the protec- 
tive properties of a CaC0 3 film are much 
less significant than is widely assumed 
(that is, in reducing dissolved oxygen at 
cathodic regions). Interestingly, Hig- 
ginson concludes that, in static air- 
saturated waters, the concentration of 
dissolved solids (such as chloride or 
sulphate ions) at constant total hardness 
(as CaCC>3) and the total hardness of the 
water both have little direct effect on 
the corrosion rate (at pH 6.5 to 8.5). 

As was the trend for the general corro- 
sion rates for the noncoated HSLA steels, 
the rates for the galvanized steel were 
higher in the air-saturated waters than 
in the deaerated waters. In deaerated 
waters, galvanized steel corrosion rates 
varied from 0.2 to 1.3 mpy (table 4). 
These rates were generally higher than 
those of either the EX-TEN-H60 or KAI- 
WELL-55 steels (except for the Urling No. 
1 and Robinhood No. 9 waters, in which 
CaC03 film formation probably did not oc- 
cur). In air-saturated mine waters, the 
galvanized steel corroded at projected 
rates ranging from 0.7 to 3.3 mpy. In 
air-saturated media, the galvanized steel 
corroded faster than the HSLA steels in 



waters from the Somerset No. 60 and Bald- 
win Mines, at about the same rate as the 
HSLA steels in the waters from the Maris- 
sa and Urling No. 1 Mines, and slower 
than the HSLA steels in waters from the 
Robinhood No. 9 and Peabody No. 10 Mines. 

Corrosion rates determined by long-term 
weight-loss tests are listed in table 5. 
Corrosion rates for the EX-TEN-H60 steel 
varied from 0.8 to 2.2 mpy, and rates 
for the KAI-WELL-55 steel varied from 1.3 
to 2.1 mpy. In these static-immersion 
tests, the KAI-WELL-55 steel did not 
exhibit the superior corrosion resistance 
observed during the electrochemical test- 
ing. The KAI-WELL-55 steel actually av- 
eraged somewhat higher corrosion rates 
than did the EX-TEN-H60 steel in all mine 
waters except those from the Peabody No. 
10 and Marissa Mines. 

In general, corrosion rates determined 
by weight loss were roughly comparable in 
magnitude to those determined electro- 
chemically in air-saturated mine waters. 
This is a reasonable result, since the 
dissolved oxygen contents from air dis- 
solution during the weight-loss tests, 
ranging from 6.3 to 7.9 ppm, were not 
greatly below the higher dissolved oxygen 
contents of the air-saturated waters used 
for the electrochemical testing (9.3 to 
10.5 ppm). The sole exception to the 
observed general comparability of corro- 
sion rates obtained by the weight-loss 
and electrochemical test methods in air- 
saturated solution was for the Peabody 
No. 10 water, where the electrochemically 
determined rates were much higher than 



TABLE 5. - Corrosion rates of HSLA Split Set steels in underground 
coal mine waters 1 as determined by weight-loss method 2 



Mine 



Oxygen 
content, 

E£S 



Corrosion rate,- 5 mpy 



EX-TEN-H60 



Av 



KAI-WELL-55 



Av 



Peabody No. 10 , 

Marissa 

Baldwin 

Somerset No. 60 , 

Urling No. 1 

Bureau of Mines Experimental. . . . . 

Robinhood No. 9 

'Test solution temperature 55° F, 
2 ASTM Standard G31-72 (5). 
3 a standard deviation. 



7.4 
7.1 
6.3 
6.8 
7.4 
7.8 
7.9 



2.2 
1.7 
.8 
.9 
1.4 
1.2 
1.8 



0.2 
.1 
.2 
.3 
.2 
.4 
.2 



2.1 
1.3 
1.6 
1.3 
2.1 
1.6 
2.1 



0.1 
.2 
.2 
.1 
.4 
.1 
.1 



11 



those determined by weight loss. The 
weight-loss rate was the highest for the 
EX-TEN-H60 steel in the Peabody No. 10 
water and at the highest rate measured 
for the KAI-WELL-55 (two other waters 
exhibited same rate). These rates, how- 
ever, unlike those for the electrochemi- 
cal testing in the same water, differed 
by only small amounts from the weight- 
loss rates obtained with the other 
waters. With the exception of the Pea- 
body No. 10 water, the long-term weight- 
loss rates did not appear to be signi- 
ficantly affected by the growing rust 
product layer. 

Localized pitting corrosion of steel is 
known to be influenced by CI" ion content 
of water. Since the waters from some 
mines were high in chloride content, pit- 
ting of the steel samples was expected 
and was commonly observed on the steel 
surfaces after the electrochemical corro- 
sion testing. Nonuniform corrosive at- 
tack was also observed on the steel sam- 
ples after the total-immersion corrosion 
tests. In an effort to evaluate the ten- 
dency of HSLA steels to suffer localized 
attack in the form of pitting or crevice 
corrosion, the cyclic polarization tech- 
nique was employed. This measurement is 
similar to a potentiodynamic anodic po- 
larization plot, except that the scan is 
reversed at some predetermined positive 
potential or current density. In gen- 
eral, the degree of hysteresis in the 
curve is indicative of the material's 
tendency to suffer localized corrosion. 
In these experiments, the scan was re- 
versed at a current density of 10 7 
nA/cm 2 . 

Typical pitting scans of HSLA steels 
are shown in figures 2A and 2B. Figure 
2A is a scan indicating moderate tendency 
of the specimen to pit, whereas figure 2B 
indicates a lesser tendency to pit. The 
protection potential (E p ) seen on these 
plots is defined as the potential at 
which the hysteresis loop of the pitting 
scan is completed, and below which (E 
more negative) pits will not initiate. 
If E p is more positive than the corrosion 
potential (E corr , the open-circuit cell 
potential), pitting becomes less likely 
to occur as E p becomes more positive rel- 
ative to E corr (4_, 6^). In figure 2A, E p 





1 

A 


1 1 1 1 1 


0.0 


- 


- 


- .2 


- 


^^j ■ 


-.4 


^corr 


J^^ - 








_ fi 




j i i i i 



< 10° I0 1 I0 2 I0 3 I0 4 I0 5 I0 6 I0 7 I0 8 



o 

a 




10* 10° 10' 10 = 

CURRENT, nA/cm 2 

FIGURE 2.— Examples of pitting scans. A, Scan exhibiting 
tendency of specimen to pit; B, scan indicating substantially 
less tendency to pit than scan A above. 



is more negative than E corr and pitting 
is expected. The pitting potential (Eq), 
also called the critical potential, has 
also been used as an indication of pit- 
ting tendency. The E p , however, is more 
reproducible and is considered to be the 
most reliable indicator (6_). 

Pitting scans were evaluated using 
three criteria: (1) the degree of hys- 
teresis displayed by the curve, (2) the 
difference between E corr and Ep, and (3) 
whether actual pitting was observed dur- 
ing laboratory testing. If the E p was 
more negative than E corr , the degree of 
hysteresis was significant, and formation 
of actual pits was observed on the test 
samples, then the pitting tendency was 
rated high. If the E p was more positive 



than E corr , but the difference between E p 
and E c was small (less than 0.1 V), the 



12 



TABLE 6. - Pitting tendency of HSLA and galvanized steels 
in underground coal mine waters 



Mine 



10. 



Peabody No. 

Marissa 

Baldwin 

Somerset No. 60. 
Urling No. 1. . . . 
Robinhood No. 9. 



KAI-WELL-55 



Deaerated 



High. 



do. 



Moderate 

High 

Moderate 
... do* . . 



Air-saturated 



High. 



do. 



• .do. 



. .do. 
. .do. 
• .do. 



Galvanized 



Deaerated 



Moderate 
High... 
• . .do. . 



...do. . 
. . . do. . 
... do. . 



Air-saturated 



High. 
Do. 
Do. 
Do. 
Do. 
Do. 



pitting tendency was arbitrarily rated as 
moderate (provided that observed pitting 
was not severe and that the pitting scans 
showed diminished hysteresis). 

Both the HSLA and galvanized steels ex- 
hibited a high tendency toward pitting in 
all the air-saturated mine waters (table 
6). As expected, pitting tendency in any 
given mine water was generally less when 
the same mine water was deaerated. The 
HSLA steel specimens exhibited a marked 
decrease in pitting tendency in deaerated 
Baldwin, Robinhood No. 9, and Urling No. 
1 Mine waters, as opposed to the high 
pitting tendency in the same waters when 
air-saturated. The pitting tendency of 
the HSLA steels in the other three mine 
waters (Marissa, Peabody No. 10, and Som- 
erset No. 60) also decreased somewhat in 
deaerated waters, as evidenced by smaller 
hysteresis loops and less pitting of lab- 
oratory test specimens. Despite this 
decline in pitting tendency, the HSLA 



steels were very susceptible to localized 
corrosive attack in all three of these 
mine waters and hence were all rated as 
having a high pitting tendency. 

Galvanized samples followed the same 
general trend exhibited by the noncoated 
HSLA steels, whereby samples corroded in 
deaerated waters showed somewhat less 
tendency to pit than those corroded in 
air-saturated waters, although the over- 
all tendency still led to five of the six 
water exposures being rated as a high 
tendency to pit. In the case of the de- 
aerated water from the Peabody No. 10 
Mine, although of the highest chloride 
content, the observed increase in pitting 
resistance was significant enough to war- 
rant a moderate pitting tendency rating. 
In tests on the galvanized steel, in all 
of the air-saturated waters, high pitting 
tendency ratings resulted, even though 
the water chloride content ranged from 
low to very high. 



CONCLUSIONS 



In the long-term weight-loss corrosion 
tests, little difference was noted be- 
tween the corrosion rates exhibited by 
EX-TEN-H60 and by KAI-WELL-55 steel, from 
which Split Set friction rock stabilizers 
are fabricated. The Cu-bearing KAI- 
WELL-55 steel had slightly less corrosion 
resistance in the Pennsylvania and West 
Virginia mine waters, but corroded at 
about the same rates as the EX-TEN-H60 
steel in the Illinois mine waters. 

In the accelerated electrochemical 
tests, the KAI-WELL-55 steel had slightly 
lower corrosion rates than the EX-TEN-H60 
steel in most of the mine waters 



tested. The electrochemically deter- 
mined corrosion rates in deaerated so- 
lutions were always lower than in cor- 
responding aerated solutions. With the 
exception of two mine waters, which were 
relatively much lower in dissolved ions 
than the other mine waters examined, it 
is believed that the precipitation of a 
protective CaC0 3 film (as evidenced by 
positive Langelier indexes) was respon- 
sible for relatively low corrosion rates 
in both aerated and deaerated waters. 
Formation of this film held electrochem- 
ical corrosion rates, which might have 
been expected to be substantially higher 



13 



than those observed, to below 2.0 mpy. 
The sole exception was the mine water 
with the highest chloride content, for 
which much higher corrosion rates were 
attributed to the corrosive attack being 
severe enough to disrupt any CaC0 3 film 
that may have tended to form. 

Corrosion rates determined by the long- 
term weight-loss tests were more compar- 
able to those determined electrochemi- 
cally in air-saturated waters than to 
rates determined electrochemically in de- 
aerated waters. 

Pitting scans using the cyclic polari- 
zation technique indicated the pitting 
tendency to be high for both the KAI- 
WELL-55 and galvanized steels in the aer- 
ated waters. The pitting tendency of the 



KAI-WELL-55 steel was somewhat reduced 
for several of the deaerated waters, as 
it was for the galvanized steel in one 
water, but the tendency was nonetheless 
at a moderate level rather than at a low 
level. This tendency toward pitting, 
which was observed during both the ac- 
celerated electrochemical testing and 
during the long-term weight-loss testing, 
was confirmed by pitting scan data and 
somewhat complicates interpretation of 
the above-reported corrosion rates. 
Since pitting can be an especially insi- 
dious and destructive form of corrosion, 
particular attention should be given to 
the pitting of installed stabilizers in 
waters of chemistry similar to those 
evaluated. 



REFERENCES 



1. Ailor, W. H. Handbook on Corro- 
sion Testing and Evaluation. Wiley, 
1971, 873 pp. 

2. American Society for Metals. 
(Cleveland, OH). Metals Handbook. 1948, 
1,332 pp. 

3. . (Metals Park, OH), Prop- 
erties and Selection: Nonferrous Alloys 
and Pure Metals. Metals Handbook, v. 2, 
9th ed. , 1979, 855 pp. 

4. American Society for Testing and 
Materials. Standard Practice for Con- 
ducting Cyclic Potentiodynamic Polariza- 
tion Measurements for Localized Corro- 
sion. ANSI/ASTM G61-78 in 1982 Annual 
Book of ASTM Standards: Part 10, Metals 
- Physical, Mechanical, Corrosion Test- 
ing. Philadelphia, PA, 1982, pp. 1,124- 
1,129. 

5. . Standard Recommended Prac- 
tice for Laboratory Immersion Corrosion 
Testing of Metals. G31-72 in 1982 ASTM 
Standards: Part 10, Metals - Physical, 
Mechanical, Corrosion Testing. Phila- 
delphia, PA, 1982, pp. 959-970. 

6. Baboian, R. , and G. S. Haynes. 
Cyclic Polarization Measurements — Experi- 
mental Procedure and Evaluation of Test 



Data. Ch. in Electrochemical Corrosion 
Testing, STP 727, ed. by F. Mansfeld and 
U. Bertocci. ASTM, 1981, pp. 274-282. 

7. Drane, C. W. Natural Waters. Ch. 
in Corrosion. V. 1 in Metal /Environment 
Reactions, ed. by L. L. Shreir. Newnes- 
Butterworths, Boston, 2d ed. , 1976, 
pp. 2:38-2:50. 

8. Higginson, A. The Effect of 
Physical and Chemical Factors on the Cor- 
rosivity of a Synthetic Mine Water. 
Counc Miner. Technol. Randberg, Repub. 
S. Afr. Mintek Rep. M140, 1984, 22 pp. 

9. Inge rs oil -Rand Co. research staff. 
Private communication, July 1981; avail- 
able upon request from A. F. Jolly III, 
BuMines, Rolla, MO. 

10. Kruger, J. New Approaches to the 
Study of Localized Corrosion. Ch. in 
Electrochemical Techniques for Corrosion, 
ed. by R. Baboian. NACE, Katy, TX, 1977, 
pp. 35-41. 

11. Lusignea, R. , J. Felleman, and 
G. Kirby. Development of a Nondestruc- 
tive Test Device for Friction Rock Sup- 
ports (contract H0202030, Foster-Miller, 
Inc.). BuMines OFR 165-83, 1983, 
135 pp.; NTIS PB 83-257519. 



14 



12. Mining Equipment International. 
Split Set Support Systems Revolutionize 
Roof Bolting. V. 5, Jan. -Feb. 1981, 
pp. 45-46. 

13. Moebs, N. N. , and R. M. Stateham. 
Geologic Factors in Coal Mine Roof 
Stability — A Progress Report. BuMines 
IC 8976, 1984, 27 pp. 

14. Peterson, W. M. , and H. Siegerman. 
A Microprocessor-Based Corrosion Measure- 
ment System. Ch. in Electrochemical Cor- 
rosion Testing, STP 727, ed. by 
F. Mansfeld and U. Bertocci. ASTM, 1981, 
pp. 390-406. 



15. Tilman, M. M. , A. F. Jolly III, 
and L. A. Neumeier. Corrosion of Fric- 
tion Rock Stabilizers in Selected Uranium 
and Copper Mine Waters. BuMines RI 8904, 
1984, 23 pp. 

16. . Corrosion of Roof Bolt 

Steels in Missouri Lead and Iron Mine Wa- 
ters. BuMines IC 9055, 1985, 9 pp. 

17. Woldman, N. E., and R. C. Gibbons. 
Engineering Alloys. Van Nostrand Rein- 
hold, 5th ed. , 1973, 1,427 pp. 



US GOVERNMENT PRINTING OFFICE 1987-605-017/60104 



INT.-BU.0F MINES,PGH.,PA. 28571 



U.S. Department of the Interior 
Bureau of Mine*— Prod, and Diutr. 
Cochrane Mill Road 
P.O. Box 18070 
Pittsburgh. Pa. 15236 



OFFICIAL BUSINESS 
PENALTY FOR PRIVATE USE, WOO 



] Do not wish to receive this 
material, please remove 
from your mailing list. 

"2 Address change. Please 
correct as indicated* 



AN EQUAL OPPORTUNITY EMPLOYER 



^i 



^% 













v 



^ O « **-/» 











p o ^ :?§»• 4-°* ■ 



°.><b 









o 









^c? 



&* 



. « ft > T- ,-Jv „ 1 * 









^ 



>^ 







'o 



-0 



^o* 



4> C 0NC 









'<? 



V^W { 



^ 



^/V ' 1 */^^,^ 





?> >Tt* A 

<U * * • 4>\ * L 



* ,0 







^ 






O "> 




* rO 



~o 









, W i 



« I T v T* e, * t> 



^V»^^^^^V«^V^,/\a 









^ v \ °- 
























y" 7 ^ 















*°** 

























♦ 









&% 






° \V^f o 






^^ 










^^ . 



«^%. °o 









C^^P 



^ v ^ 
















!5?%JS55&^^^^&i55F5J 


























r ^^. 








^*' 







VV 



V 3 % ^ 

^j -j <, ^ 




i ".:V'"/.<-A 



heckman i±ii / *?\ ifmfj ^ v ^ws; ^ v % ifS^i .^ v '. wr-? ^\ \wm 



HECKMAN 

BINDERY INC. 

^^ SEP 92 

, ^HS|^ N. MANCHESTER, 
^S*^ INDIANA 46962 



Z 



*-UM" v * <J 













-V 



r>. *. 




4> -O **l. 







*-^ 







